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Basis of Presentation and Significant Accouting Policies (Basis of Presentation) (Details) $ / shares in Units, $ in Millions | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2018 USD ($) advertiser publisher | Sep. 30, 2017 USD ($) | May 11, 2018 | Dec. 31, 2017 | Sep. 28, 2017 $ / shares | Jul. 31, 2012 USD ($)
HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% |  |  |  |  |
Surplus notes | $ 499.0 |  |  |  |  | $ 503.0
MediaAlpha |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) | 62.20% |  |  | 64.40% |  |
Number of advertisers | advertiser | 600 |  |  |  |  |
Number of publishers | publisher | 330 |  |  |  |  |
Preferred Stock | HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) | 96.90% |  |  | 96.90% |  |
Common Stock | HG Global |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) | 88.40% |  |  | 88.40% |  |
Restricted Stock |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Payments related to tax withholding for share-based compensation | $ 8.4 | $ 9.2 |  |  |  |
OneBeacon |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Business acquisition, share price | $ / shares |  |  |  |  | $ 18.10 |
NSM Insurance HoldCo, LLC |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 95.00% |  |  |

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